This document summarizes steps for creating a shopping cart in a Rails application. It covers generating a Cart model and LineItem model with relationships, using Rails sessions to associate the cart with each user, adding public and private methods, callbacks and validations, adding a button to add items to the cart, and modifying views and controllers. Testing is done to ensure functionality. Homework includes enhancing the functionality by adding a click handler, session counter, and conditional display.

1. Cart Creation

2. What we’ll coverUsing SessionsPublic, Private, and Protected Methods in RubyRelationships between modelsActive Record Callbacks & ValidationAdding a button to a pageMore Functional Testing

3. Generate a shopping cartrails generate scaffold cartNo foreign keys presentOnly one of the tables has a foreign keyNeed to recover the cart with every request

4. Rails SessionsBy default, session info stored in a browser session cookie (4k limit)Database or memcached also availableDon’t store data that can easily be outdatedSerialized ActiveRecordobjectsCryptographically signed but unencryptedDon’t store critical information solely in the session

5. Associate the cart with a sessionapp/controllers/application_controller.rbprivatedefcurrent_cartCart.find(session[:cart_id])rescue ActiveRecord::RecordNotFound cart = Cart.create session[:cart_id] = cart.id cart end

6. Public, Private, & Protected MethodsDifferent from Java & C#Public methods can be invoked by anyone Private methods accessible by an object from a derived classProtected methods accessible by other objects & objects from derived classesInheritance doesn’t determine method visibilityPrivate & protected methods visible from subclasses

7. Storing items in the cartrails generate scaffold line_itemproduct_id:integercart_id:integerBy convention, singular of table name appended with “_id”Need to establish relationship in both the database and the modelModel declarations add ability to build and navigate the relationship

8. ActiveRecord relationshipsOne to Onehas_one :containedbelongs_to :containerOne to Manyhas_many :containedbelongs_to :containerTable with foreign keys has the ‘belongs_to’

9. Add Relationship Specifiersclass Cart < ActiveRecord::Basehas_many :line_items, :dependent => :destroyendclass LineItem < ActiveRecord::Basebelongs_to :productbelongs_to :cartendclass Product < ActiveRecord::Basehas_many :line_itemsend

10. What if we destroy a cart?Line_items dependent on cart:dependent => :destroy indicates that line_items are destroyed along with the cartdestroy involves ActiveRecord validation logic, delete only removes from the database

11. What if we destroy a product?Make sure it isn’t contained in a cart

12. ActiveRecord Callbacks & ValidationsCallbacks invoked before & after operationsFor example save, delete, create, validateCan view unformatted data in ‘before’ callbacksDates & CurrencyReturning the actual value ‘false’ stops the operationAdd a handler or define as a method

13. Add a buttonWon’t be creating a new controller or a new actionCreating an item in the cart, so use line_item controllerLooking at generated code in line_item_controller.rb, we’ll use the ‘Create’ action‘Create’ action called using HTTP Postbutton_to‘button label’, ‘URL Path’, ‘HTML options’Add ‘_path’ to controller to get URL path (i.e. line_item_path)Pass in hash values to URL path as parametersid extracted from ActiveRecord objects passed inapp/views/store/index.html.erb<%= button_to ‘Add to Cart’, line_items_path(:product_id => product) %>

14. Modify line_item createBy default, create parameter is a serialized line_item object - params[:line_item]Create a line_item based on the product id and add it to the cart

15. Modify line_item create (cont.)app/controllers/line_items_controller.rb

16. Update the functional testtest/functional/line_items_controller_test.rbassigns() accesses instance variables in the controller being tested

17. Try it outhttp://localhost:3000/Cart scaffolding didn’t show any attributes of what was just added

18. Modify the viewapp/views/cart/show.html.erb<h2>Your Pragmatic Cart</h2><ul> <% for item in @cart.line_items %> <li><%= item.product.title %></li> <% end %></ul>

19. Try it out (again)http://localhost:3000/Cart now shows what is containedNeed to show each item only once (next chapter)

20. HomeworkChange the view so that clicking on a book’s image will also add the product to the cartAdd a new session variable to record how many times the user accessed the store controller’s index actionAdd the counter to the template and display it on top of the catalog pageReset the counter to zero when adding to the cartChange template to display counter when > 5